1. Field of the Invention
The present invention relates to an AAL terminal system and a synchronization method between the respective terminal systems when the terminal system AAL1 (ATM Adaptation Layer Type 1) for converting STM (Synchronous Transfer Mode) data to ATM (Asynchronous Transfer Mode) cells has a duplex configuration of an acting system and a standby system.
2. Description of the Related Art
Japanese Patent Publication Laid-Open (Kokai) No. Heisei 9-55752 discloses a synchronization system of duplex STM/ATM converters capable of switching free from momentary break due to information lack, duplication, or the like, in switching between an operating device as an acting system and an operating system as a standby system.
The synchronization system of the duplex STM/ATM converters disclosed in this Japanese Patent Publication Laid-Open No. 9-55752 is provided with an intervenient signal line for connecting an STM/ATM converter of the acting system and an STM/ATM converter of the standby system, input STM frame pulse counters (for example, 376 counter) for counting the pulses of input STM frames, and head frame number storing memories for storing the input STM frame pulse count values of the input STM frame pulse counters at the beginning of cell assemble when the SN (Sequence Number) value of the AAL1 header is xe2x80x9c0xe2x80x9d, the input STM frame pulse counter and the head frame number storing memories being provided in the respective systems.
In synchronization, a standard FP count value of the input STM frame pulse counter is sent from the STM/ATM converter of the acting system to the STM/ATM converter of the standby system via the intervenient signal line. The standby STM/ATM converter sets the input STM frame pulse counter to the received value and synchronizes the input STM frame pulse counters of the both systems. Each cell head frame number of the channels to be sequentially synchronized is read from the cell head frame number storing memory in the standby STM/ATM converter and the read value is compared with the current FP count value. At a coincidence, input of the STM data of the channel into the cell assemble buffer starts, which makes the output ATM cells of the acting STM/ATM converter coincident with the output ATM cells of the standby STM/ATM converter. Hereinafter, the same procedure will be sequentially performed on all the channels, so to synchronize the acting system and the standby system.
According to the method, the STM store states of the cell assemble buffers of the acting system and the standby system can be in good agreement without any momentary break of main signals, and an acting system and a standby system can be switched without any data lack, or data duplication.
The above-mentioned synchronization method, however, in which synchronization is sequentially performed on every channel, is defective in that it takes much time to complete the synchronization on all the channels when there are a lot of channels.
An object of the present invention is to provide a duplex configuration system and a synchronization method for an AAL terminal device for converting STM data to ATM cells, in which synchronization can be performed in a short time when switching the both systems without any cell lack or duplication.
Another object of the present invention is to improve the reliability of service by establishing synchronization in a short time when switching the both systems without any cell lack or duplication.
According to one aspect of the invention, a synchronization method of an AAL terminal system of a duplex configuration including an acting ALL (ATM Adaptation Layer Type) terminal device and a standby ALL terminal device, for converting STM data into ATM cells, wherein
the acting ALL terminal device and the standby ALL terminal device comprise frame pulse counters with the predetermined count value set therein in every user connection of STM network;
in the acting AAL terminal device having received a cell conversion starting request,
starting cell conversion, notifying the starting timing of the cell conversion to the standby AAL terminal device, and starting count of input STM frame pulses by the frame pulse counter;
in the standby AAL terminal device having received the starting timing of the cell conversion,
starting count of the input STM frame pulses by the frame pulse counter of the corresponding user connection,
wherein establishing synchronization between output ATM cells of the acting device and output ATM cells of the standby device in each user connection by the frame pulse counter.
In the preferred construction, the acting AAL terminal device continues to notify the timing to the standby AAL terminal device every time the frame pulse counter counts the predetermined count value until stopping the cell conversion.
In another preferred construction, the AAL terminal device is an AAL 1 (ATM Adaptation Layer Type 1) terminal device.
In another preferred construction, the predetermined count value set in the frame pulse counter corresponds to the speed of each user connection of the STM network.
In another preferred construction, the acting AAL terminal device continues to notify the timing to the standby AAL terminal device every time the frame pulse counter counts the predetermined count value, until stopping the cell conversion; while
the standby AAL terminal device starts the cell conversion at the time when the count value of the frame pulse counter gets to the predetermined count value.
According to another aspect of the invention, a terminal system of a dual configuration including an acting AAL terminal device and a standby AAL terminal device, which comprises converting means for converting STM data to ATM cells, control means, and a serial bus for connecting the both devices through the control means, wherein
the respective control means comprising
a plurality of frame pulse counters with predetermined count values set therein, in every user connection of the STM network;
the control means of the acting AAL terminal device comprising
means for directing the converting means to start cell conversion upon receipt of a cell conversion starting request,
means for directing the frame pulse counter to count input STM frame pulses at the same time of starting the cell conversion, and
means for notifying the starting timing of the cell conversion to the standby AAL terminal device through the serial bus; while
the control means of the standby AAL terminal device comprising
means for directing the frame pulse counter of the standby device to start counting the input STM frame pulses, upon receipt of the timing, and
means for directing a start of cell conversion at the time when the count value of the frame pulse counter gets to the predetermined count value.
In the preferred construction, the acting control means notifies the starting timing of the cell conversion to the standby AAL terminal device every time when the frame pulse counter counts the predetermined count value.
In another preferred construction, the AAL terminal device is an AAL 1 (ATM Adaptation Layer Type 1) terminal device.
In another preferred construction, the predetermined count value set in the frame pulse counter corresponds to the speed of each user connection of the STM network.
Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow.